Then pick the option to Select Suppressed, then right click on one of them in the tree & click Unsuppress. This of course will select every suppressed so if there are some that you don't want unsuppressed you will need to CTRL un-select them in the tree.
You didn't mention if you were trying to unsuppress components in an assembly, or unsuppress features in a part. I'm not sure if it affects anyone's answers.
I found my own answer but not really what I'm looking for...
Pick the mates from the tree then choose unsuppress icon from the context menu.
I was hoping that somewhere in the Modify Configurations dialog box would have an "untick all" or "tick all" button.